pattrstorage: delete stored value

I am hoping there is a way to do the opposite of setstoredvalue. In other words delete a stored value at a particular slot for a particular client object.

I am resorting to inserting a place-holder datum using setstoredvalue to indicate that that position is 'empty' or null, but it isn't very satisfactory.

I notice that in the storage window you can manually delete values and leave white space. How could I do that with a message to pattrstorage? i've tried " " and this does not work